The invention relates generally to strips of brads useable in fastener driving tools, and more particularly to improvements in obliquely collated strips of brads, useable in power trim nailers, and methods for making the same.
The arrangement of brads in an obliquely collated strip, sometimes referred to as an angled strip of brads or merely as angled brads, for use in fastener driving tools having an aftwardly swept magazine is known generally. An exemplary fastener driving tool designed for angled brads is disclosed in the referenced co-pending U.S. Application entitled "Pneumatic Trim Nailer", assigned commonly and incorporated herein by reference.
A strip of angled brads comprises generally a plurality of brads, for example 50 or so brads, arranged adjacently and offset axially so that the angle of the collated strip corresponds generally to an angle between the magazine and a nose-piece channel of the tool. More specifically, the brads forming the collated strip are arranged so that an edge formed by adjacent head portions of the collated strip has substantially the same angular relationship to the longitudinal axis of the brads as the channel of the nose-piece has to the magazine. The plurality of brads are cohered by an adhesive material, like nitrocellulose, or alternatively by other frangible binding means, so that individual brads are separable from the collated strip during operation of the tool. An exemplary angled strip of brads is disclosed in the referenced co-pending U.S. Application entitled "Angled Chisel Point Brad And Method Therefor", also assigned commonly and incorporated herein by reference.
The collated strip of brads is disposed in the magazine of the tool and biased toward the nose-piece so that a leading endmost brad of the collated strip is disposed in the channel thereof. To install, or set, a brad, a gas or pneumatically powered driver blade is accelerated axially through the channel from behind the leading endmost brad and into engagement with a head portion thereof. The driver blade moves the leading endmost brad axially thus separating, or shearing, the brad from the collated strip. The remaining brads of the collated strip are retained in the tool magazine by a hardened shearing block, which engages an underside of the head portions thereof, as the driver blade shears the leading endmost brad therefrom. The sheared brad is then discharged from the nose-piece of the tool into a target material or workpiece.
The predominant force that must be overcome by the driver blade when shearing brads from the collated strip is that resulting generally from the adhesive or other binding means. Thus the pressure available to operate the driver blade is generally specified to provide an adequate but limited driving force for this purpose. The operating pressure is generally a characteristic of the tool, and depends on many variables including, among others, the particular type of tool, and whether the tool is hot or cold. The operating pressure may also vary among tools of the same manufacture and model. A known angled brad trim nailing tool, available from ITW Paslode, Vernon Hills, Ill., for example, operates in a pressure range between approximately 79 psi and approximately 102 psi. Other trim nailing tools operate at other pressures, which may be higher or lower.
Occasionally, the driver blade is unable to shear the leading endmost brad from the collated strip, resulting in misfiring of the tool. The inventors of the present invention have recognized that the occasional inability of the driver blade to shear brads from the collated strip results from a tendency for the head portion of adjacent brads to become interlocked during the manufacture thereof. Misfiring thus occurs when the driver blade is unable to overcome the adhesive or other forces binding the brads of the collated strip and any additional forces resulting from the interlocking of adjacent head portions. It is thus desirable to eliminate or at least substantially reduce the interlocking of adjacent brads, since the additional force required to shear interlocked brads from the collated strip sometimes prevents the shearing of the brads, and in any event detracts from the force available to drive the brads into the workpiece.
FIG. 5 illustrates one known prior art process for forming head portions on a plurality of wires 2 cohered in an angled strip 10. The strip of wires 10 is clamped between opposing portions of a gripper die 20 as a stepped header punch 30 applies one or more axial blows to end portions 14 of the wires 2 in a heading operation. The header punch 30 has a plurality of step and riser portions 32 and 34 that form head portions on corresponding wires 2 as the header punch 30 engages the strip 10. During the heading operation, the wire end portions 14 expand radially outwardly from the axis of the corresponding wire 2, as indicated by arrows 15. The radially expanding wire end portions 14 however tend to deform asymmetrically when struck by the header punch 30, and more particularly the radial expansion of the wire end portions 14 tends to be skewed toward the leading ends 3 of the wires 2. This tendency results from the strip of wires 10 having an angled edge 16 along the wire end portions 14 relative to the stepped portions 32 of the header punch 30.
The tendency for adjacent head portions to interlock during formation thereof is further complicated, or aggravated, by any misalignment between the steps of the header punch and the corresponding wires. This misalignment results generally from variation in wire diameter, and produces head portions that are misaligned, or out of registry, with the corresponding brad shanks. The interlocking of adjacent head portions tends also to be more severe in applications where the cohered strip of wires is pre-flattened, wherein the individual wires thereof have a generally elongated racetrack, rather than a round or circular, sectional shape. The racetrack sectional shape of pre-flattened, or merely flattened, wire is characterized generally by at least two opposing substantially parallel portions and two opposing curved portions. The substantially parallel portions may be straight and parallel or may have a generally arcuate shape.
The referenced co-pending U.S. Application entitled "Angled Chisel Point Brad And Method Therefor" discloses an alternative header die configuration having angled step portions for forming head portions 50 with a flatter top surface relative to the longitudinal axis of the brad shank. FIG. 5 of the present application illustrates the prior art header punch 30 having angled step portions 33, shown in phantom lines. This alternate header die configuration having angled step portions 33 alone, however, has no significant or appreciable effect toward lessening the interlocking of adjacent head portions.
FIG. 6 is a prior art angled strip of brads 40 having a plurality of brads 42 with corresponding leading and trailing ends 44 and 46 and a corresponding head portion 50. The adjacent head portions 50 are formed overlappingly, or interlockingly, in a manner that requires an increased driving force from the tool driver blade to shear individual brads from the cohered strip 40. Generally, the leading side 44 of the brad head portions 50 has a bulge extending interlockingly into the trailing side 46 of an adjacent brad head portion 50. The interlocking bulge results from the tendency of the head portion to form asymmetrically during the heading operation, as discussed above. The interlocking bulge of the head portions is a curved, generally S-shaped surface, which is approximated in FIG. 6 by first, second and third linear interface portions 52, 53 and 54 between adjacent head portions 50. The first and third interface portions 52 and 54 of the bulge have a generally positive upwardly extending slope, and the intermediate second interface portion 53 of the bulge has a generally negative downwardly extending slope.
In operation, the head portions 50 of all but the leading endmost brad 51 of the strip 40 are supported on a magazine shearing block 60, which prevents the brads in the cohered strip 40 from moving axially as the driver blade shears the leading endmost brad 51 therefrom. More particularly, an upper outermost corner 61 of the shearing block 60 digs into the underside of the brad adjacent the driver blade to prevent the remaining brads in the strip 40 from moving backwardly into the magazine, in a direction opposite the feed direction, during the shearing operation. Thus to shear the leading endmost brad from the strip, the driver blade must overcome the forces imposed by the interlocking adjacent head portions 50, and more particularly energy from the driver blade must be expended to deform the adjacent head portions to shear the endmost brad 51, since the strip cannot move backwardly to allow passage of the head of the endmost brad.
In collated strips of brads cohered by adhesives, the adhesive covers the brads from the head to tip portions thereof. Misfiring therefore tends to occur more frequently in longer brads cohered by adhesive, since a greater adhesive binding force must be overcome by the driver blade, and less interlocking is required to increase the binding force of adjacent brads beyond the shearing capacity of the driver blade. In the Paslode angled brad trim nailing tool operating in a pressure range between approximately 79 and 102 psi, misfiring begins to occur when installing adhesive coated brads having interlocking head portions with a length of two inches or more, and is particularly troublesome with interlocking brads with a length of two and one-half inches or more. In prior art angled brads having interlocking head portions, the bulge may extend forwardly of the leading side of the brad by as much as 0.011 inches or more.
The present invention is drawn toward advancements in the art of angled strips of brads useable in power trim nailing tools.
It is an object of the invention to provide novel angled strips of brads, useable in power trim nailing tools, and novel methods therefor that overcome problems in the art.
It is another object of the invention to provide novel angled strips of brads, and novel methods for the manufacture thereof, that are reliable and economical.
It is another object of the invention to provide novel angled strips of brads and novel methods for the manufacture thereof having improved performance, and more particularly angled strips of cohered brads from which individual brads are relatively reliably and consistently shearable in power trim nailing tools, and angled strips of brads that require relatively less force to shear brads from the cohered strip.
It is a further object of the invention to provide novel angled strips of brads, especially angled strips of brads cohered by adhesives, and novel methods for the manufacture thereof that have relatively reduced interlocking between adjacent brads, and that are less prone to misfire from power trim nailing tools.
It is another object of the invention to provide novel methods for manufacturing novel angled strips of brads having relatively reduced interlocking between adjacent head portions thereof by biasing a leading side of the head portions of the brads rearwardly toward trailing sides of the brads during a head forming, or heading, operation.
It is yet another object of the invention to provide novel methods for manufacturing novel angled strips of brads having relatively reduced interlocking between adjacent head portions thereof by forming head portions with a relatively reduced bulge protruding forwardly from a leading side of the brad.
It is a more particular object of the invention to provide a novel angled strips of brads comprising generally a plurality of brads having a shank with a tip portion. A head portion of at least some of the plurality of brads having a bulge protruding forwardly from the leading side thereof and extending at least partially into the trailing side of the head portion of an adjacent brad. An upper leading side portion of the head portions of the plurality of brads offset rearwardly of the leading side of the shank, whereby interlocking of adjacent head portions of the angled strip of brads is reduced.
It is another more particular object of the invention to provide novel methods for manufacturing novel angled strips of brads formed by biasing a leading side of the head portions of the plurality of flattened wires rearwardly toward a trailing side of the plurality of flattened wires with a riser portion of a header punch, and preferably with a rearwardly sloped riser portion of a header punch.
These and other objects, aspects, features and advantages of the present invention will become more fully apparent upon careful consideration of the following Detailed Description of the Invention and the accompanying Drawings, which may be disproportionate for ease of understanding, wherein like structure and steps are referenced generally by corresponding numerals and indicators.